Electric power conversion circuit system

ABSTRACT

There is provided an electric power conversion circuit system having a primary side electric power conversion circuit, a secondary side electric power conversion circuit, and a control circuit. The control circuit sets at least one of a half-bridge phase difference between a lower-left-arm transistor and a lower-right-arm transistor of the primary side electric power conversion circuit and a half-bridge phase difference of the secondary side electric power conversion circuit based on OFF periods of the primary side and secondary side electric power conversion circuits, dead-times of the primary side and secondary side electric power conversion circuits, and an amount of change of a power supply voltage so that a current in a non-transmission period of electric power is zero between the primary side and secondary side electric power conversion circuits.

PRIORITY INFORMATION

This application claims priority to Japanese Patent Application No.2014-035186 filed on Feb. 26, 2014, which is incorporated herein byreference in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to an electric power conversion circuitsystem, and in particular, to an electric power conversion circuitsystem having a plurality of input/output ports.

2. Related Art

JP 2012-125040 A proposes an electric power conversion circuit system inwhich two types of circuits are integrated, taking advantage ofmagnetically coupled reactors showing different inductances in thecurrent directions. The system has a structure in which coupled reactorsare placed on both ends of a transformer, and are connected tofull-bridge circuits. In this structure, a maximum of four directcurrent ports are provided in one circuit. When electric power istransmitted between the left and right full-bridge circuits connected onthe respective ends of the transformer, if the duty ratios (Duty) arethe same, high-efficiency electric power transmission is possible.

As described above, the electric power can be transmitted with highefficiency from one full-bridge circuit to the other if the duty ratiosof the left and right full-bridge circuits are the same. However, whenthe duty ratios differ from each other, a current during anon-transmission period is increased, and the conversion efficiency issignificantly reduced. Therefore, there is a restriction to set equalduty ratios between the left and right full-bridge circuits, which meansthat the voltage value of the direct current port connected to theintermediate point of the transformer cannot be arbitrarily selected.

In view of the above, the present inventors have proposed controlling ahalf-bridge phase difference between half-bridge circuits forming thefull-bridge circuit, so that the reduction of the conversion efficiencycan be inhibited even when the duty ratios differ between thefull-bridge circuits. However, in this related art that was proposed(not yet made public at the time of filing of the present application)also, the advantages may be insufficient, and a further improvement inefficiency is desired. In particular, there is a problem in that theefficiency may be reduced when there is a dead-time period or when thepower supply voltage changes.

The present invention advantageously provides an electric powerconversion circuit system having a plurality of input/output ports, thatcan transfer the electric power with high efficiency even during adead-time period or even when the power supply voltage changes.

SUMMARY

According to one aspect of the present invention, there is provided anelectric power conversion circuit system comprising: a primary sideelectric power conversion circuit; a secondary side electric powerconversion circuit magnetically coupled to the primary side electricpower conversion circuit; and a control circuit that controlstransmission of electric power between the primary side electric powerconversion circuit and the secondary side electric power conversioncircuit. The primary side electric power conversion circuit comprises,between a primary side positive electrode bus and a primary sidenegative electrode bus, a left arm, a right arm, and a primary sidecoil, wherein the left arm comprises an upper-left-arm transistor and alower-left-arm transistor connected in series, the right arm comprisesan upper-right-arm transistor and a lower-right-arm transistor connectedin series, and the primary side coil is connected between a connectionpoint of the left arm and a connection point of the right arm. Thesecondary side electric power conversion circuit comprises, between asecondary side positive electrode bus and a secondary side negativeelectrode bus, a left arm, a right arm, and a secondary side coil,wherein the left arm comprises an upper-left-arm transistor and alower-left-arm transistor connected in series, the right arm comprisesan upper-right-arm transistor and a lower-right-arm transistor connectedin series, and the secondary side coil is connected between a connectionpoint of the left arm and a connection point of the right arm. Thecontrol circuit sets at least one of a half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the primary side electric power conversion circuit and a half-bridgephase difference between the lower-left-arm transistor and thelower-right-arm transistor of the secondary side electric powerconversion circuit based on OFF periods of the primary side electricpower conversion circuit and the secondary side electric powerconversion circuit and based on dead-times of the primary side electricpower conversion circuit and the secondary side electric powerconversion circuit, so that, when a duty ratio between the left arm andthe right arm of the primary side electric power conversion circuitdiffers from a duty ratio between the left arm and the right arm of thesecondary side electric power conversion circuit, a current between theprimary side electric power conversion circuit and the secondary sideelectric power conversion circuit is zero in a non-transmission periodof the electric power.

According to another aspect of the present invention, preferably, thecontrol circuit sets at least one of the half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the primary side electric power conversion circuit and thehalf-bridge phase difference between the lower-left-arm transistor andthe lower-right-arm transistor of the secondary side electric powerconversion circuit based further on an amount of change of an inputvoltage.

According to another aspect of the present invention, preferably, thecontrol circuit sets the half-bridge phase difference between thelower-left-arm transistor and the lower-right-arm transistor of theprimary side electric power conversion circuit based on the OFF periodof the secondary side electric power conversion circuit, and the controlcircuit sets the half-bridge phase difference between the lower-left-armtransistor and the lower-right-arm transistor of the secondary sideelectric power conversion circuit based on the OFF period and thedead-time of the primary side electric power conversion circuit.

According to another aspect of the present invention, preferably, thecontrol circuit sets the half-bridge phase difference between thelower-left-arm transistor and the lower-right-arm transistor of theprimary side electric power conversion circuit based on the OFF periodof the secondary side electric power conversion circuit, and the controlcircuit sets the half-bridge phase difference between the lower-left-armtransistor and the lower-right-arm transistor of the secondary sideelectric power conversion circuit based on the OFF period and thedead-time of the primary side electric power conversion circuit, and onthe amount of change of the input voltage.

According to another aspect of the present invention, preferably, theprimary side coil comprises a coil and a transformer-primary side coilmagnetically coupled to each other, and the secondary side coilcomprises a transformer-secondary side coil and a coil connected to anintermediate point of the transformer-secondary side coil.

According to another aspect of the present invention, preferably, theprimary side coil comprises a transformer-primary side coil and a coilconnected to an intermediate point of the transformer-primary side coil,and the secondary side coil comprises a coil and a transformer-secondaryside coil magnetically coupled to each other.

According to various aspects of the present invention, electric powercan be transferred between the primary side and the secondary side withhigh efficiency even during the dead-time period and even when the powersupply voltage changes. In addition, according to various aspects of thepresent invention, the number of magnetic elements through which analternating current passes can be reduced and the conversion efficiencycan be improved.

The present invention will be more clearly understood with reference tothe embodiment described below. The embodiment, however, is describedfor more clearly understanding the invention, and is not intended tolimit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the present invention will be described indetail with reference to the following figures, wherein:

FIG. 1 is a diagram of a circuit system structure presumed in apreferred embodiment of the present invention;

FIG. 2 is a functional block diagram of an OFF period δ determinationprocessor and a half-bridge phase difference γ determination processorin FIG. 1;

FIG. 3 is a diagram of a circuit system structure of a preferredembodiment of the present invention;

FIG. 4 is a functional block diagram of an OFF period δ determinationprocessor and a half-bridge phase difference γ determination processorof FIG. 3;

FIG. 5 is a timing chart in a preferred embodiment of the presentinvention;

FIG. 6 is an explanatory diagram of an ON-OFF control in a period [1];

FIG. 7 is an explanatory diagram of an ON-OFF control in a period [2];

FIG. 8 is an explanatory diagram of an ON-OFF control in a period [3];

FIG. 9 is an explanatory diagram of an ON-OFF control in a period [4];

FIGS. 10A and 10B are explanatory diagrams of a waveform when there isno dead-time correction term;

FIGS. 11A and 11B are explanatory diagrams of a waveform when there is adead-time correction term;

FIG. 12 is an explanatory diagram of a waveform when a power supplyvoltage is increased;

FIG. 13 is an explanatory diagram of a waveform when a power supplyvoltage is reduced;

FIGS. 14A and 14B are explanatory diagrams of a waveform when there isno voltage change correction term;

FIGS. 15A and 15B are explanatory diagrams of a waveform when there is avoltage change correction term;

FIG. 16 is a diagram of a circuit system structure in another preferredembodiment of the present invention; and

FIG. 17 is a diagram of a circuit system structure in yet anotherpreferred embodiment of the present invention.

DETAILED DESCRIPTION

Preferred embodiments of the present invention will now be describedwith reference to the drawings. The electric power conversion circuitsystem according to the preferred embodiments of the present inventionmay be equipped in, for example, electricity-driven vehicles such as ahybrid electric vehicle and an electric automobile, but the presentinvention is not limited to such configurations.

<Presumed Circuit System>

First, a circuit system presumed in the present embodiment will bedescribed.

FIG. 1 shows an electric power conversion circuit system presumed in thepresent embodiment. The electric power conversion circuit system 8 hasan electric power conversion device 10 and a control circuit 50. Theelectric power conversion device 10 has four input/output ports; twoinput/output ports A˜D are selected from the four input/output ports,and electric power is converted between the two selected input/outputports. The electric power conversion device 10 has a primary sideelectric power conversion circuit 20 and a secondary side electric powerconversion circuit 30, and the primary side electric power conversioncircuit 20 and the secondary side electric power conversion circuit 30are magnetically coupled to each other by a transformer 40.

A primary side left arm 23 and a primary side right arm 27 are connectedin parallel to each other between a primary side positive electrode bus60 and a primary side negative electrode bus 62. The primary side leftarm 23 includes a primary side upper-left-arm transistor 22 and aprimary side lower-left-arm transistor 24 connected in series to eachother. The primary side right arm 27 includes a primary sideupper-right-arm transistor 26 and a primary side lower-right-armtransistor 28 connected in series to each other.

The input/output port A (PORT_A) is provided between the primary sidepositive electrode bus 60 and the primary side negative electrode bus62. The input/output port C (PORT_C) is provided between the primaryside negative electrode bus 62 and a center tap which is a connectionpoint of coils 42 and 43. The secondary side electric power conversioncircuit 30 has a similar structure. Loads and power supplies areconnected to the input/output ports A, B, C, and D.

The transformer 40 includes a primary side coil 39 and a secondary sidecoil 49. The primary side coil 39 is formed by coils 41˜44 connected inseries, and the secondary side coil 49 is formed by coils 45˜48connected in series. The coils 41 and 44 forma coupling reactor on theprimary side, and the coils 45 and 48 form a coupling reactor on thesecondary side.

The control circuit 50 sets various parameters for controlling theelectric power conversion circuit 10, and executes switching control ofswitching transistors of the primary side electric power conversioncircuit 20 and the secondary side electric power conversion circuit 30.The control circuit 50 includes an electric power conversion modedetermination processor 51, a phase difference φ determination processor52, an OFF period δ determination processor 54, a half-bridge phasedifference γ determination processor 56, a primary side switchingprocessor 58, and a secondary side switching processor 59.

The electric power conversion mode determination processor selects, fromamong the input/output ports A˜D, two input/output ports, based on amode signal from outside (not shown), and sets a mode for electric powerconversion between the two selected input/output ports. One of theelectric power conversion modes is a bidirectional electric powertransmission mode between the input/output port A and the input/outputport B (this mode will hereinafter be referred to as an insulatingconverter mode). The other electric power conversion modes are modes inwhich the voltage is increased or decreased between the input/outputports A and C, or between the input/output ports B and D (these modeswill hereinafter be referred to as voltage increasing/decreasingconverter modes).

The phase difference φ determination processor 52 sets a phasedifference φ of switching periods of switching transistors between theprimary side electric power conversion circuit 20 and the secondary sideelectric power conversion circuit 30 so that the electric powerconversion device 10 may function as a DC-to-DC converter circuit. Thephase difference φ is a phase difference of voltage waveforms of atwo-end voltage V₁ of the primary side coil 39 and a two-end voltage V₂of the secondary side coil 49.

The OFF period δ determination processor 54 sets an OFF period δ (dutyratio) of the switching transistor of the primary side electric powerconversion circuit 20 and the secondary side electric power conversioncircuit 30 so that the primary side electric power conversion circuit 20and the secondary side electric power conversion circuit 30 may functionas a voltage increasing/decreasing circuit.

The half-bridge phase difference γ determination processor 56 sets ahalf-bridge phase difference of the primary side electric powerconversion circuit 20 and a half-bridge phase difference of thesecondary side electric power conversion circuit 30 so that acirculating current during a non-transmission period is zero even whenthe phase difference φ of the voltage waveforms of the two-end voltageV₁ and the two-end voltage V₂ is zero and the duty ratios of the voltagewaveforms differ between the primary side and the secondary side. Thehalf-bridge phase difference on the primary side is a phase differenceof switching control between the primary side left arm 23 and theprimary side right arm 27 (phase difference between half-bridges), andmore specifically, is a phase difference of the switching controlbetween the primary side lower-left-arm transistor 24 and the primaryside lower-right-arm transistor 28. The half-bridge phase difference γ2on the secondary side is a phase difference of switching control betweenthe secondary side left arm 33 and the secondary side right arm 37(phase difference between half-bridge circuits), and more specifically,is a phase difference of the switching control between the secondaryside lower-left-arm transistor 34 and the secondary side lower-right-armtransistor 38.

The primary side switching processor 58 applies switching control of theswitching transistors of the primary side left arm 23 and the primaryside right arm 27 based on outputs of the electric power conversion modedetermination processor 51, the phase difference φ determinationprocessor 52, the OFF period δ determination processor 54, and thehalf-bridge phase difference γ determination processor 56.

The secondary side switching processor 59 applies switching control ofthe switching transistors of the secondary side left arm 33 and thesecondary side right arm 37 based on outputs of the electric powerconversion mode determination processor 51, the phase difference φdetermination processor 52, the OFF period δ determination processor 54,and the half-bridge phase difference γ determination processor 56.

FIG. 2 shows a functional block diagram of the OFF period δdetermination processor 54 and the half-bridge phase difference γdetermination processor 56. In FIG. 2, an asterisk (*) indicates acommand value.

The OFF period δ determination processor 54 adds a value determined byapplying a feed-forward control using a relationship formula2π(1−V_(C)/V_(A)*) for a voltage command value V_(A)* and a voltagevalue V_(C), and a value Δδ₁ determined by applying a PI control basedon the voltage value V_(A), to determine an OFF period command value(primary side duty command value) δ₁* of the primary side electric powerconversion circuit 20. In addition, the OFF period δ determinationprocessor 54 adds a value determined by applying a feed-forward controlusing a relationship formula 2π(1−V_(D)/V_(B)*) for a voltage commandvalue V_(B)* and a voltage value V_(D) and a value Δδ₂ determined byapplying a PI control based on the voltage value V_(B), to determine anOFF period command value (secondary side duty command value) δ₂* of thesecondary side electric power conversion circuit 30. With thisconfiguration, even if there is a change in the loads connected to theinput/output ports A and B, the OFF period command values (duty commandvalues) δ₁* and δ₂* can be determined in consideration of the voltagevalues V_(A) and V_(B) which have changed with the change of the loads.

The half-bridge phase difference γ determination processor 56 determinesa half-bridge phase difference command value γ₁* on the primary sideusing a relationship formula γ_(1l *=)2π−δ₂*. The half-bridge differenceγ determination processor 56 also determines a half-bridge phasedifference command value γ₂* on the secondary side using a relationshipformula γ₂*=2π−δ₁*.

The control circuit 50 may be realized by an ECU having a processor anda memory and that executes a computer program stored in a programmemory. The processes may be distributed over a plurality of processors,or a part of the functions of the control circuit 50 may be realized bya dedicated hardware.

Operations of two modes; that is, the voltage increasing/decreasingconverter mode, and the insulating converter mode in such a circuitsystem structure will now be described.

First, in the voltage increasing/decreasing converter mode, for example,when the input/output port C and the input/output port A on the primaryside are considered, the input/output port C is connected to anup-and-down connection point of the primary side left arm 23 via thecoils 41 and 42 of the primary side coil 39. Because the ends of theprimary side left arm 23 are connected to the input/output port A, avoltage increasing/decreasing circuit would be connected between theinput/output port C and the input/output port A. In addition, theinput/output port C is connected to an up-and-down connection point ofthe primary side right arm 27. Because the ends of the primary sideright arm 27 are also connected to the input/output port A, anothervoltage increasing/decreasing circuit would be connected between theinput/output port C and the input/output port A. Thus, two voltageincreasing/decreasing circuits are connected in parallel to each otherbetween the input/output port C and the input/output port A. Similarly,in the secondary side electric power conversion circuit 30 also, twovoltage increasing/decreasing circuits are connected in parallel in theleft and right arms 33 and 37, between the input/output port D and theinput/output port B.

Next, in the insulating converter mode, if the input/output port A onthe primary side and the input/output port B on the secondary side areconsidered, the primary side coil 39 is connected to the input/outputport A, and the secondary side coil 49 is connected to the input/outputport B. Therefore, by adjusting a phase difference φ of the switchingperiod of the primary side electric power conversion circuit 20 and thesecondary side electric power conversion circuit 30, it is possible toconvert the electric power which is input to the input/output port A andtransmit the converted electric power to the input/output port B, or toconvert the electric power which is input to the input/output port B andtransmit the converted electric power to the input/output port A. Inother words, if the two-end voltage V₁ of the primary side is anadvanced phase with respect to the two-end voltage v2 on the secondaryside, the electric power can be transmitted from the primary sideelectric power conversion circuit 20 to the secondary side electricpower conversion circuit 30, and, if the two-end voltage V₂ on thesecondary side is an advanced phase with respect to the two-end voltageV₁ on the primary side, the electric power can be transmitted from thesecondary side electric power conversion circuit 30 to the primary sideelectric power conversion circuit 20.

In the insulating converter mode, when the primary side duty commandvalue δ₁* and the secondary side duty command value δ₂* are the same,there is no problem. However, when the duty command values differbetween the primary side and the secondary side, the two-end voltage V₁on the primary side and the two-end voltage V₂ on the secondary sidehave different voltage waveforms, and, even if the phase difference φ isset to 0, electric power would be transmitted between the primary sideelectric power conversion circuit 20 and the secondary side electricpower conversion circuit 30, and the transmission cannot be controlledby the adjustment of the phase difference φ. This causes a restrictionin that the duty ratio of the primary side and the duty ratio of thesecondary side must always be set equal to each other.

However, by calculating the primary side half-bridge phase differencecommand value based on the relationship formula of γ₁*=2π−δ₂* andcalculating the secondary side half-bridge phase difference commandvalue using the relationship formula of γ₂*=2π−δ₁*; that is, by settingthe primary side half-bridge phase difference command value inconsideration of the secondary side duty command value and setting thesecondary side half-bridge phase difference command value inconsideration of the primary side duty command value, it becomespossible to set the voltage waveforms of the two-end voltages V₁ and V₂to be the same even when the duty command values differ between theprimary side and the secondary side. This means that, with thisconfiguration, there is no restriction that the duty ratios must be setequal between the primary side and the secondary side.

The above-described system is the presumed circuit structure system, andthe present embodiment further improves such a circuit structure system.

<Circuit Structure System of Present Embodiment>

FIG. 3 shows an electric power conversion circuit system 8 of thepresent embodiment presuming the circuit system structure describedabove. In addition to the structure of FIG. 1, a correction termdetermination processor 57 is added to the control circuit 50.

An example configuration will be described in which a direct currentpower supply is connected to the input/output port B on the secondaryside, and electric power is transmitted to the input/output port A onthe primary side.

As shown in FIG. 4, the correction term determination processor 57 is afunctional block that corrects the half-bridge phase difference commandvalue calculated by the half-bridge phase difference γ determinationprocessor 56, and further corrects the half-bridge phase differencecommand values calculated using relationship formulae γ₁*=2π−δ₂* andγ₂*=2π−δ₁*. Specifically, as the voltage waveforms of the two-endvoltages V₁ and V₂ may change during the dead-time period or due to achange in the input voltage, resulting in different voltage waveforms,the half-bridge phase difference command values are corrected inconsideration of influences of these, to more precisely coincide thevoltage waveforms of the two-end voltages V₁ and V₂.

The correction term determination processor 57 specifically determines acorrection term based on the following formula:Δγ₂ =dt·ω _(SW)+(2π−δ₁*){1−NV _(A) /V _(B))   (1)where dt represents the dead-time, ω_(SW) represents a switching anglefrequency, N represents a ratio of number of windings of the transformer40, V_(A) represents the primary side voltage, and V_(B) represents thesecondary side voltage.

The correction term determination processor 57 then applies thecorrection by adding the correction term to the command value calculatedby γ₂*=2π−δ₁*. In other words, the correction term determinationprocessor 57 calculates the half-bridge phase difference command valueusing the relationship formulae:

γ₁^(*) = 2Π − δ₂^(*) $\begin{matrix}{\gamma_{2}^{*} = {{2\Pi} - \delta_{1}^{*} + {\Delta\gamma}_{2}}} \\{= {{2\Pi} - \delta_{1}^{*} + {{dt} \cdot \omega_{sw}} + {( {{2\Pi} - \delta_{1}^{*}} )( {1 - {{NV}_{A}/V_{B}}} )}}}\end{matrix}$The first term on the right side of the above-described formula (1) is acorrection term corresponding to the dead-time, and the second term onthe right side is a correction term corresponding to a change of theinput voltage.

Next, the correction term Δγ₂ will be described in detail, separatelyfor the first term and the second term on the right side of the formula.

<First Term on Right Side: Dead-Time Correction Term>

FIG. 5 shows operation waveforms of switching transistors when electricpower is transmitted from the secondary side to the primary side. InFIG. 5, S1˜S4 correspond to the switching transistors 22, 24, 26, and 28of the primary side electric power conversion circuit 20, and S5˜S8correspond to the switching transistors 32, 34, 36, and 38 of thesecondary side electric power conversion circuit 30 (refer to FIG. 1) .In FIG. 5, “S1 S2” represents a switching timing of S1and S2. Theswitching transistors S1and S2 are alternately switched ON and OFF. Thedescriptions of “S3, S4”, “S5, S6”, and “S7, S8” are similar to theabove. The description of “NV₁” represents a voltage waveform shown by aproduct of the primary side voltage; that is, the two-end voltage V₂,and the number of windings of the transformer N, “V₂” represents avoltage waveform of the two-end voltage V₂ on the secondary side, and“i_(u),” represents a current on the primary side.

A hatched portion corresponds to the dead-time period. In FIG. 5, thephase difference φ and the length λ of the dead-time period are alsoshown. In addition, periods [1]˜[4] are shown as examples.

FIG. 6 shows ON-OFF states of the switching transistors S1˜S8 in theperiod [1] of FIG. 5. The switching transistors S1, S4, S5, and S8 re inthe ON state, and the other switching transistors are in the OFF state.The flow of current in this case is as shown in FIG. 6. On the secondaryside (power sending side), because the switching transistors S5 and S8are ON, a current flows from S5 to the coils 46 and 47 and further to S8(S5→46, 47→S8). Similarly, on the primary side (power receiving side),because the switching transistors S1 and S4 are ON, a current flows fromS4 to the coils 42 and 43 and further to S1 (S4→42, 43→S1).

FIG. 7 shows ON-OFF states of switching transistors S1 S8 in the period[2] of FIG. 5. The switching transistors S1, S4, and S8 are in the ONstate, and the other switching transistors are in the OFF state. In theperiod [2] , compared to the period [1], the switching transistor S5 istransitioned from the ON state to the OFF state. When S5 on thesecondary side (power sending side) is switched OFF, a current continuesto flow through a diode connected in parallel to S6, and the two-endvoltage V₂ on the secondary side is reduced to zero. Therefore, theON-OFF of S5 of the upper arm determines the two-end voltage V₂ on thesecondary side (power sending side).

FIG. 8 shows ON-OFF states of the switching transistors S1˜S8 in aperiod [3] of FIG. 5. The switching transistors S1, S4, S6, and S8 arein the ON state, and the other switching transistors are in the OFFstate.

FIG. 9 shows ON-OFF states of the switching transistors S1˜S8 in aperiod [4] of FIG. 5. The switching transistors S4, S6, and S8 are inthe ON state, and the other switching transistors are in the OFF state.In the period [4], compared to the period [3], the switching transistorsS1 is transitioned from the ON state to the OFF state. When S1 on theprimary side (power receiving side) is switched OFF, a current continuesto flow through a diode connected in parallel to S1, and the two-endvoltage V₁ on the primary side does not become zero unless S2 isswitched ON. Therefore, the ON-OFF of S2 on the lower arm determines thetwo-end voltage V₁ on the primary side (power receiving side).

Normally, in a circuit system having a half-bridge circuit as shown inFIG. 3, a dead-time of a few hundreds of nanoseconds to a fewmicroseconds is provided, so that the upper and lower switchingtransistors are not short-circuited. This is the reason why, in FIG. 5,dead-time periods are provided in which S1 and S2 are both switched OFF,S3 and S4 are both switched OFF, S5 and S6 are both switched OFF, and S7and S8 are both switched OFF. On the other hand, when the dead-time isprovided, as described above, the arms that determine the two-endvoltages V₁ and V₂ of the transformer 40 differ between the powersending side and the power receiving side. Therefore, a difference iscaused in the pulse width between the two-end voltages V₁ and V₂.Specifically, the pulse width on the secondary side (power sending side)is trimmed by the dead-time dt (the pulse width is reduced) as comparedto the pulse width on the primary side (power receiving side).

Therefore, in order to realize a same waveform for the two-end voltagesV₁ and V₂, the trimmed dead-time dt may be added to the pulse width ofthe two-end voltage V₂ on the secondary side (power sending side) .Specifically, a dead-time correction term may be set as:

Dead-time correction term=dt·ω _(SW)

FIGS. 10A and 10B show a result of a computer simulation of voltagewaveforms of the two-end voltages V₁ and V₂ and a current i_(u) on theprimary side when there is no dead-time correction term. These figuresshow a result in a case where dt≠0, D₁>D₂, and the number of windings=N.FIG. 10A shows the waveforms of the two-end voltages V₁ and V₂, and FIG.10B shows a waveform of the primary side current i_(u). It should benoted that the duty ratios on the primary side and the secondary sidediffer from each other. As can be understood from FIG. 10A, a differenceis caused in the pulse width between NV₁ and V₂ as shown by “a” in FIG.10A, and the pulse width is reduced for V₂. As can be understood fromFIG. 10B, even when the two-end voltages V₁ and V₂ are zero, the primaryside current iu is not set to zero, and a circulating current is causedin the non-transmission period. The circulating current is a currentcirculating in the primary side during the non-transmission periodbecause the energy accumulated in an inductor during the transmissionperiod cannot be fully output from the port on the primary side.Occurrence of such a circulating current results in reduction of theconversion efficiency.

In contrast, FIGS. 11A and 11B show the voltage waveforms of the two-endvoltages V₁ and V₂ and the current i_(u) on the primary side when thereis a dead-time correction term. FIG. 11A shows the waveforms of thetwo-end voltages V₁ and V₂, and FIG. 11B shows a waveform of the primaryside current i_(u). As can be understood from FIG. 11A, the differencein the pulse width between NV₁ and V₂ is corrected compared to FIG. 10Aas shown by “a” in FIG. 11A, and the waveforms are approximately equalto each other. As can be understood from FIG. 11B, the circulatingcurrent in the non-transmission period is inhibited, and the conversionefficiency is improved.

<Second Term on Right Side: Voltage Change Correction Term>

With a change of the power supply voltage connected to the input/outputport B also, a difference may be caused in the voltage waveforms of thetwo-end voltages V₁ and V₂, and a circulating current may be generated.

FIG. 12 shows voltage waveforms and the waveform of the primary sidecurrent i_(u) when the power supply voltage V_(B) of the input/outputport B is increased and NV₁<V₂. The upper part shows the voltagewaveforms of V₂ and NV₁, and the lower part shows the current waveformof i_(u). As shown in the lower part, a circulating current is caused inthe non-transmission period.

FIG. 13 shows the voltage waveforms and the waveform of the primary sidecurrent i_(u) when the power supply voltage V_(B) of the input/outputport B is reduced and NV₁>V₂. The upper part shows the voltage waveformsof V₂ and NV₁, and the lower part shows the current waveform of i_(u).In this case also, as shown in the lower part, a circulating current iscaused in the non-transmission period.

As described, when the power supply voltage is increased or decreased, acirculating current is caused. In order to inhibit the circulatingcurrent as shown in FIGS. 12 and 13, a total sum of the amount of changeof the current in periods [1]˜3] of FIGS. 12 and 13 may be set to zero.A pulse width correction necessary for setting the total sum to zero maybe determined by:Voltage change correction term=(2π−δ₁*)(1−NV _(A) /V _(B))NV_(A)/V_(B) represents an amount of change of the input power supplyvoltage V_(B) and the voltage change correction term is set according tothe amount of change of the power supply voltage.

FIGS. 14A and 14B show a result of a simulation when there is no voltagechange correction term and the power supply voltage V_(B) connected tothe input/output port B is reduced. FIG. 14A shows the waveforms of thetwo-end voltages V₁ and V₂, and FIG. 143 shows the waveform of thecurrent i_(u). A circulating current is caused in the non-transmissionperiod.

FIGS. 15A and 15B show a result of a simulation when there is a voltagechange correction term and the power supply voltage V_(B) connected tothe input/output port B is reduced. FIG. 15A shows the waveforms of thetwo-end voltages V₁ and V₁, and FIG. 15B shows the waveform of thecurrent i_(u). The circulating current is inhibited even in thenon-transmission period. This is similarly applicable for the case wherethe power supply voltage V_(B) connected to the input/output port B isincreased.

As described, in the present embodiment, the half-bridge phasedifference command value is corrected using the dead-time correctionterm and the voltage change correction term in the condition when theprimary side and the secondary side operate with different duty ratios.With such a configuration, even when there is a dead-time period or evenwhen the power supply voltage changes, the circulating current in thenon-transmission period can be inhibited and the conversion efficiencycan be improved.

In the case where the power supply voltage is controlled, and there isno voltage change or the voltage change is sufficiently small that thevoltage change may be ignored, the half-bridge phase difference commandvalue may be corrected with only the dead-time correction term. In thiscase, the correction is:Δγ₂ =dt·ω _(SW)This is also clear in the above-described formula (1) showing that, whenthere is no change in the power supply voltage, NV_(A)=V_(B a)t thephase difference cp of zero and the voltage change correction term whichis the second term on the right side is zero.

In addition, in the present embodiment, the half-bridge phase differencecorrection value γ₂* on the secondary side is corrected. Alternatively,the half-bridge phase difference command value γ₁* on the primary sideMay be corrected based on the dead-time and the amount of change of thepower supply voltage, to realize equal voltage waveforms, or both thehalf-bridge phase difference command values γ₁* and γ₂* on the primaryside and the secondary side may be corrected to realize equal voltagewaveforms.

Moreover, in the present embodiment, when electric power is transmittedbetween the primary conversion circuit 20 and the secondary conversioncircuit 30, the electric power passes through three magnetic elementsincluding the coupling reactors 41 and 44, the primary side andsecondary side coils 42, 43, 46, and 47, and coupling reactors 45 and48, joule-heat is increased and a current ripple is increased in thecontrol between the half-bridges. In consideration of this, as shown inFIG. 16, a configuration may be employed in which the coupling reactors45 and 48 are omitted, a reactor 100 is connected to a connection pointof the transformer-secondary side coils 46 and 47, an L value necessaryfor a one-side voltage increasing/decreasing converter mode and theinsulating converter mode is realized by one of the coupling reactors 41and 44, and the other voltage increasing/decreasing converter mode isrealized by the reactor 100, so that the number of magnetic elementsthrough which an alternating current passes is reduced and theconversion efficiency is further improved. In addition, with thereduction of the number of magnetic elements, there is an advantage thatthe circuit design is simplified. Alternatively, in FIG. 3, the couplingreactors 41 and 44 may be omitted and a reactor 100 may be connected toa connection point of the transformer-primary side coils 42 and 43. FIG.17 shows a circuit system structure in this configuration. In summary,the coupling reactor on one of the primary side electric powerconversion circuit 20 and the secondary side electric power conversioncircuit 30 may be omitted, and a reactor may be connected to theconnection point of the transformer coils in place thereof.

What is claimed is:
 1. An electric power conversion circuit system,comprising: a primary side electric power conversion circuit; asecondary side electric power conversion circuit magnetically coupled tothe primary side electric power conversion circuit; and a controlcircuit that controls transmission of electric power between the primaryside electric power conversion circuit and the secondary side electricpower conversion circuit, wherein the primary side electric powerconversion circuit comprises, between a primary side positive electrodebus and a primary side negative electrode bus, a left arm, a right arm,and a primary side coil, wherein the left arm comprises anupper-left-arm transistor and a lower-left-arm transistor connected inseries, the right arm comprises an upper-right-arm transistor and alower-right-arm transistor connected in series, and the primary sidecoil is connected between a connection point of the left arm and aconnection point of the right arm, the secondary side electric powerconversion circuit comprises, between a secondary side positiveelectrode bus and a secondary side negative electrode bus, a left arm, aright arm, and a secondary side coil, wherein the left arm comprises anupper-left-arm transistor and a lower-left-arm transistor connected inseries, the right arm comprises an upper-right-arm transistor and alower-right-arm transistor connected in series, and the secondary sidecoil is connected between a connection point of the left arm and aconnection point of the right arm, and the control circuit sets at leastone of a half-bridge phase difference between the lower-left-armtransistor and the lower-right-arm transistor of the primary sideelectric power conversion circuit and a half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the secondary side electric power conversion circuit based on OFFperiods of the primary side electric power conversion circuit and thesecondary side electric power conversion circuit and based on dead-timesof the primary side electric power conversion circuit and the secondaryside electric power conversion circuit, so that, when a duty ratiobetween the left arm and the right arm of the primary side electricpower conversion circuit differs from a duty ratio between the left armand the right arm of the secondary side electric power conversioncircuit, a current between the primary side electric power conversioncircuit and the secondary side electric power conversion circuit is zeroin a non-transmission period of the electric power.
 2. The electricpower conversion circuit system according to claim 1, wherein thecontrol circuit sets at least one of the half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the primary side electric power conversion circuit and thehalf-bridge phase difference between the lower-left-arm transistor andthe lower-right-arm transistor of the secondary side electric powerconversion circuit based further on an amount of change of an inputvoltage.
 3. The electric power conversion circuit system according toclaim 1, wherein the control circuit sets the half-bridge phasedifference between the lower-left-arm transistor and the lower-right-armtransistor of the primary side electric power conversion circuit basedon the OFF period of the secondary side electric power. conversioncircuit, and the control circuit sets the half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the secondary side electric power conversion circuit based on the OFFperiod and the dead-time of the primary side electric power conversioncircuit.
 4. The electric power conversion circuit system according toclaim 2, wherein the control circuit sets the half-bridge phasedifference between the lower-left-arm transistor and the lower-right-armtransistor of the primary side electric power conversion circuit basedon the OFF period of the secondary side electric power conversioncircuit, and the control circuit sets the half-bridge phase differencebetween the lower-left-arm transistor and the lower-right-arm transistorof the secondary side electric power conversion circuit based on the OFFperiod and the dead-time of the primary side electric power conversioncircuit, and on the amount of change of the input voltage.
 5. Theelectric power conversion circuit system according to claim 1, whereinthe primary side coil comprises a coil and a transformer-primary sidecoil magnetically coupled to each other, and the secondary side coilcomprises a transformer-secondary side coil and a coil connected to anintermediate point of the transformer-secondary-side coil.
 6. Theelectric power conversion circuit system according to claim 1, whereinthe primary side coil comprises a transformer-primary side coil and acoil connected to an intermediate point of the transformer-primary sidecoil, and the secondary side coil comprises a coil and atransformer-secondary side coil magnetically coupled to each other.